Routines to transform between canvas coordinates and world coordinates.
proc setXYRanges { {xmin 0.0} {ymin 0.0} {xmax 1.2} {ymax 1.0} } {
Set the ranges (in world units) for the x- and y-coordinates.
proc setXYScales { } {
Sets the world->canvas scales so that the full range will fit on the canvas with a few pixels to spare.
proc setXYTics { {dx 0.2} {dy 0.2} } {
Set the tic-mark spacing for the x- and y-coordinates.
proc canvasX { worldX } {
proc canvasY { worldY } {
proc worldX { canvasX } {
proc worldY { canvasY } {